In order to prevent collisions that may occur while driving a vehicle such as a car, a radar device that is capable of detecting obstacles in the vicinity (e.g., pedestrians, other vehicles, etc.) may be mounted on the vehicle. If an obstacle near the vehicle is detected, the radar device of the vehicle provides detection information on the obstacle to a driver. In response, the driver may appropriately control the vehicle, for example, by stopping the vehicle. Additionally, a control device of the vehicle may receive the detection information on the obstacle from the radar device and automatically control the vehicle without manual operation of the driver.
A radar device for such vehicles may be implemented with a pulse radar, a FMCW (Frequency Modulated Continuous Wave) radar, a spread spectrum radar, or the like. Among these radars, the pulse radar is defective in that, due to high power transmission, it is difficult to detect an object at close ranges and achieve high resolution. Also, the FMCW radar is defective in that, due to continuous signal transmission, interference with other radar signals may occur. On the other hand, the spread spectrum radar, which may use a PN (Pseudo-Noise) sequence or the like as a spectrum spread sequence, is advantageous in that it is possible to achieve a high resolution and suppress frequency interference.
However, if the spread sequence that is used in one spread spectrum radar device mounted on a vehicle is identical to the spread sequence that is used in another spread spectrum radar device mounted on another vehicle, interference may occur between such spread spectrum radar devices. For example, if spread spectrum radar devices that are mounted, respectively, on a vehicle travelling on the road on the ground and another vehicle travelling on an overpass road (or an underground road) use an identical spread sequence, interference may occur between radar signals transmitted from the spread spectrum radar devices, which may lead to errors in detecting obstacles. Therefore, it is necessary to prevent interference between radar signals transmitted from radar devices, which are mounted on vehicles travelling on roads of different heights.